The present invention relates to sensors, particularly in hydrocarbon sensors, and more particularly to electrochemical hydrocarbon sensors for exhaust monitoring, such as for on-board monitoring and evaluation of the performance of catalytic converters.
Pollution due to the extensive use of internal combustion engines and industry has long been a problem. In the last few decades numerous exhaust purification and emission control systems have been developed. In the automotive arena, preeminent among the current exhaust purification (emission control) systems for internal combustion engines are the catalytic converters.
In recent years, regulations have been instituted which require automobile makers to incorporate comprehensive on-board diagnostic systems into new vehicles. The intent of these regulations is to ensure that the vehicle operator is informed when emission control systems (i.e., the catalytic converter) are no longer performing adequately. Once operators are informed of a malfunction, they will be required to take the vehicle in for repairs so that exhaust emissions are again within the standards set by regulations. Hydrocarbon emissions are currently the main target for control, with an emissions detection limit of 25 parts per million (ppm) in the exhaust stream desired. Currently, there is no hydrocarbon sensor suitable for automobile emissions monitoring, and thus there is a need for a hydrocarbon sensor which has good sensitivity, longevity, and low cost.
The present invention provides a solution for this need by providing a solid-state electrochemical hydrocarbon sensor which offers several advantages for exhaust gas monitoring. Among the properties of the hydrocarbon sensor of this invention are sensitivity, robustness (longevity), and low cost. The invention involves materials and sensor arrangements for a solid-state electrochemical sensor which can be used to monitor hydrocarbon exhaust emissions and which can be used for on-board monitoring of catalytic converters. The sensor of the present invention comprises a proton conducting electrolyte sandwiched between two electrodes, one electrode of which is covered with an appropriate catalyst which catalyzes hydrogen liberation from non-methane hydrocarbons. A protective cover is also used on the assembly and an integrated oxygen pump is employed to remove cross-sensitivities.